by allocating a larger buffer. Test the gethostname return value for
being >= 0, not == 0, for BeOS. Don't exhaust memory if gethostname
returns an error and ENAMETOOLONG isn't defined.
[ENAMETOOLONG] (xgethostname): If gethostname
returns an error other than buffer overflow, exit with an error
message instead of allocating infinite amounts of space.
[!EXIT_FAILURE] (EXIT_FAILURE): New macro.
<errno.h>: New include.
[!errno] (errno): New declaration.
